1. Field of the Invention
The invention relates to a device for tempering a test fluid.
2. Description of the Background of the Invention
Test devices are used for example in the pharmaceutical industry to test the disintegration or dissolution of pharmaceutical substances in a test fluid, see for example DE 203 05 443 U1, DE 201 17 255 U1, U.S. Pat. No. 6,484,595. In conventional test devices, a beaker filled with test fluid is kept in a water bath which is kept at the desired test temperature by means of a heating element and a feedback control, see for example DE 83 36 233 U1 and DE 38 04 688 A1. However, the use of a water bath has a series of disadvantages. It takes a long time for the water bath to be heated to the desired test temperature. The temperature control has a considerable time lag which means that during testing deviations from the desired temperature can occur. Furthermore, for hygiene reasons, regular laborious emptying, cleaning and re-filling of the water bath are necessary. Finally, the temperature of the test fluid can be determined during testing only indirectly by measuring the temperature of the water bath which results in a systematic measuring inaccuracy.
DE 35 20 034 C1, EP 0 746 750 B1 and DE 199 23 918 A1 disclose devices in which heating is effected by means of a heating sleeve surrounding the container for the test fluid, whereby there is no need to provide a water bath. However, this type of heating also has a significant time lag owing to the necessary heat transfer through the container which generally consists of glass. In addition, the heating sleeve has a negative effect on the ability to inspect the test fluid.
DE 201 17 255 U1 discloses a device for controlling the temperature of a test fluid having a metallic pot which can be heated by means of a heating plate and is to be filled with water and into which the container for the test fluid can be inserted, wherein evaporation of the water from the metallic pot is counteracted by means of a sealing sleeve. This construction is comparatively complicated and is additionally prone to errors since it is easy to forget to fill the metallic pot with water, which is required for effective heat contact. Also, owing to the transfer of the thermal heat through the metallic pot and through the wall of the test fluid container, the feedback control is comparatively slow. Finally, owing to the arrangement of the temperature sensor in the region of the heating plate, the measured temperature does not correspond to the temperature of the test fluid.
WO 01 07890 A2 discloses in one embodiment a microtitre plate having depressions which include a metal piece loosely placed on the base of the depression. An induction coil is disposed beneath the microtitre plate for the inductive heating of the metal piece. The heating of the water in the depressions is controlled by means of a temperature control unit.
GB 2 232 902 A discloses a device for separating and measuring the liquid and solid phases of drill samples. In one embodiment, the drill sample is placed into a distillation vessel consisting of steel. Induction flows are produced in the walls of the distillation vessel by means of an induction coil disposed around the distillation vessel and this vessel is consequently heated in order to distil off the liquid components. The heating of the distillation vessel is thermostatically controlled to a temperature of 500° C.±38° C. by means of a temperature sensor disposed in contact with the base of the distillation vessel.
JP 58 112055 A describes a transparent container consisting of glass or a synthetic material for heating a fluid, wherein a magnetic body, which produces heat by means of high-frequency induction, is incorporated in the wall of the container.
U.S. Pat. No. 5,232,667 discloses a temperature control system having a resistive heating element for a sample insert in an electrochemical diagnosis system for biological samples. EP 1 811 471 A1 relates to an inductive heating unit for preserved foodstuffs in a vending machine. US 2008 0011336 A1 discloses an induction device for heating clean water flowing through a pipe. JP 2009 072746 A discloses a stirring device having an impellor, which can be inductively heated and consists of steel, and a temperature control function. JP 2005 168648 A discloses a cooking vessel which can be inductively heated. JP 2004 281250 A discloses a temperature control unit for an inductive heating device for heating a fluid stored in a tank.